This invention relates to a pneumatic boosters and, particularly to pneumatic boosters of the kind including a housing, a power piston and flexible diaphragm assembly partitioning the interior of the housing into two chambers, a poppet valve mechanism for selectively connecting or disconnecting communication between the two chambers and disconnecting or connecting communication between one of the two chambers and a reference pressure, an input rod for actuating the poppet valve mechanism and an output rod connected to the power piston.
The poppet valve mechanism conventionally comprises a plunger connected to the inner end of the input rod, a valve body having an axial bore for slidably receiving the plunger, a resilient valve member for cooperating with coaxial valve seats provided respectively on the valve body and the plunger such that when the valve member is separated from the valve seat on the valve body the two chambers are communicated and when the valve member is separated from the valve seat on the plunger one of the two chambers is communicated with a reference pressure. The valve body is connected to or integral with the power piston. The relative axial displacement of the plunger and the valve body is restricted by a restricting member.
The pneumatic booster of the kind aforementioned, generally operates satisfactorily. However, there are shortcomings such that, in actuating the booster, the input rod is sometimes moved excessively inwardly until the restricting member acts to restrict the excessive movement of the plunger relative to the valve body, thereby producing impacting sounds and stopping suddenly the inward movement of the input rod, thereby impairing the feeling in actuating the input rod, and that in releasing the input force applied on the input rod, the input rod and the plunger sometimes retract too quickly until the restricting member acts to restrict the excessive movement of the plunger. Impacting sounds will also be produced and the feeling in operating the input rod also will be impaired.